The present invention relates to a device using a piezoelectric/electrostrictive film, particularly to the structure of a piezoelectric/electrostrictive device for improving the operational characteristic of an element for converting electrical energy into mechanical energy such as mechanical displacement, mechanical force, or vibration and vice versa. Specifically, the present invention relates to a piezoelectric/electrostrictive device to be applied to each transducer, various actuators, frequency-region functional components (filters), transformers, vibrators and resonators for communication and motive power, oscillators, discriminators, and various sensors including ultrasonic sensors, acceleration sensors, angular velocity sensors, impact sensors, and mass sensors, and moreover unimorph- and bimorph-type elements used for servo shift elements described in "From foundation up to application of piezoelectric/electrostrictive actuator" written by Kenji Uchino {edited by Japan Industrial Technique Center and published by MORIKITA SHUPPAN (transliterated)}, and to be preferably adopted to various actuators used for mechanisms for shift and positioning adjustment and angle adjustment of various precision components and, optical equipment and precision equipment.
Recently, a shift control element for adjusting an optical-path length or position on the sub-micron order has been requested in optical and magnetic recording fields and the precision-machining field. To respond to this request, development of a piezoelectric/electrostrictive actuator or the like is progressed which is an element using a displacement based on the reverse piezoelectric effect or electrostrictive effect caused by applying an electric field to a piezoelectric/electrostrictive material such as a ferroelectric.
In the magnetic recording field which uses hard disc drives, storage capacity has been remarkably increased in recent years. This is because the a recording medium is used more efficiently by increasing the number of recording tracks to increase the recording density in addition to improvements in of recording methods.
This attempt has been mainly made so far on the improvement of a voice coil motor. Moreover, as a new technical art, an attempt has been made to apply an electrostatic-type microactuator fabricated by the micromachine process of Si or Ni to the tracking system of a hard-disk magnetic head is described on pp. 1081-1084 in the preliminary manuscript collection of "1997 International Conference on solid-state Sensors and Actuators" of "TRANSDUCER' 97".
Moreover, Japanese Patent Application Laid-Open No. 10-136665 discloses a piezoelectric actuator as shown in FIG. 16 in which a fixed portion 103, a movable portion 104, and at least one beam portion 102 for connecting the portions 103 and 104 to each other are integrally formed by forming at least one hole on a flat body made of a piezoelectric/electrostrictive material, and a strain generation portion is constituted by forming an electrode layer 105 on at least a part of at least one beam portion 102 so that an expansion or a contraction motion occurs in the direction connecting the fixed portion 103 with the movable portion 104, and a displacement mode of the movable portion 104 to the fixed portion 103 generated due to the expansion or contraction motion of the strain generation portion is an arc-shaped or rotational mode in the plane of the flat body.
However, in the case of the conventional art for positioning a recording head mainly using a voice coil motor, it is difficult to accurately position a recording head so as to accurately trace tracks when the number of tracks increases in order to correspond to further increase in capacity.
The above-described technical art using an electrostatic-type microactuator obtains a displacement by applying a voltage between a plurality of flat electrodes formed through micromachining. However, it is difficult to raise a resonance frequency because of the structure. Consequently, the technical art includes such problems that vibrations are not easily attenuated when a high-speed operation is performed and the positioning accuracy is deteriorated. Moreover, there is a feature that the technical art is displacement-theoretically inferior in the linearity of the voltage-displacement characteristic. Therefore, there are many problems to be solved from the viewpoint of accurate alignment. Furthermore, the process of micromachining itself has a problem from the viewpoint of manufacturing cost.
Furthermore, in the case of a piezoelectric actuator disclosed in Japanese Patent Application Laid-Open No. 10-136665, the piezoelectric-operation portion has a monomorph structure. Therefore, the main-strain axis of a piezoelectric film becomes coaxial or parallel with the main-shift axis of the piezoelectric-operation portion. Thus, there are problems that the piezoelectric-operation portion itself generates only a small shift and the movable portion also has a small displacement. Moreover, the piezoelectric actuator itself is heavy and subject to harmful vibrations for operation such as residual vibrations and vibrational noises under a high-speed operation as described in Japanese Patent Application Laid-Open No. 10-136665 and therefore, it is necessary to suppress harmful vibrations by injecting a filler into a hole. However, the use of such a filler may exert a bad influence upon a displacement of the movable portion. Moreover, because it is unavoidable to constitute a piezoelectric actuator with a piezoelectric/electrostrictive material inferior in mechanical strength, there is a problem that the actuator is subject to restriction concerning material strength, which in turn inhibits choice of shape and.